Handbook of Genetic Counseling/Chorionic Villus Sampling (CVS)

Chorionic Villus Sampling (CVS)

Introduction

Discuss the reason for referral.
Elicit prior knowledge about CVS.
Elicit knowledge about AMA or other indications for session.
Assess concerns and set goals for the session.
Provide overview of topics for counseling session.

Client & Partner Information

Discuss why it's important to get pregnancy, personal, and family history.
Go over pregnancy history:
- G?P?
- LMP? EDC?
- Infertility?
- Exposures?
- Medical complications?
- How has the pregnancy been going?
Personal background:
- Occupation?
- Religion?
- Ethnicity?
- Chronic illness?
- Partner exposure?

Elicit Family History

Construct pedigree:
- Abnormal # miscarriages, stillbirths, infant deaths?
- Previous children with chromosome abnormality, NTD, Down syndrome, birth defects, mental retardation?
- Consanguinity?
- Other concerns/risk factors?

What is AMA?

Woman is age 35 & above at expected date of delivery.
As maternal age increases, risks of birth defects increase.
Women do not make new eggs like males make sperm.
They are born will all the eggs they will have in their life and these eggs mature with age.
There are procedures that can be done to assess the risk, but there are also risks associated with the procedures.
The age of 35 is the "magic" number because this is when the risk of the procedure is justified.
The background risk for major birth defects for women of all ages is 3-5%.

Explain Chromosome Abnormalities

Explain cells, chromosome, and DNA
Show karyotypes
Explain nondisjunction
Show abnormal karyotypes (trisomy 13, 18, 21, sex chromosome anomalies)
Give a general description of the clinical features and prognoses.
- Trisomy 18 & 13 are most severe with most affected dying before the age of 1 year
- Trisomy 21 is more mild; characteristic physical features and mild to moderate MR
- Turner and Kleinfelter's syndromes are sex chromosome anomalies. Also usually mild.

Quote Risks

Show charts to figure risk of chromosome abnormalities.
Give age-specific risks:
- Age at CVS: ____________
- Down syndrome: 1 in _______ ( %)
- Any CA: 1 in ________ ( %)

Discuss the option of CVS

What is it?
- CVS is short for chorionic villus sampling
- The chorionic villi are wisps of fetal tissue or finger-like projections that attach the pregnancy sac to the uterine wall
- CVS is the technique in which this sample of placental tissue is obtained
- The technique has been around for approximately 15 years although methods have changed over time
- It is unique because it is used to diagnose certain birth defects in the 1st trimester of pregnancy rather than later in the pregnancy like amniocentesis
  - It is usually performed at 10-12 weeks gestation
What can it tell me?
- CVS can detect certain abnormalities in the fetus
  - General chromosome abnormalities
  - Specific genetic disorders that have been previously identified
- It can determine the sex of the baby.
What can it NOT tell me?
- CVS cannot detect neural tube defects such as spina bifida
  - For this reason, it may be useful to measure the amount of AFP in the maternal serum at 15-18 weeks gestation
  - Also, follow-up with US at 18-20 weeks is recommended
- It cannot detect all birth defects or mental retardation
  - For example, congenital heart defects, cleft lip & palate cannot be seen.
  - Also the severity of the defect cannot be known from CVS
Exactly what does the procedure involve?
- Show figures of CVS
- Transcervical CVS:
  - Done at 10-12 weeks gestation
  - A speculum is inserted and the vagina and cervix are cleaned with betadeine
  - Some physicians apply a tenaculum to the lip of the cervix which can be painful
  - Using US to guide, a thin tube is guided into the placenta
  - Gentle suction is applied to the tube to remove the villi
  - This method is easiest to perform when the placenta is posterior and close to the cervix
  - A larger sample is taken as compared to transvaginal CVS
  - Discomfort is often minimal, perhaps similar to a pap smear
  - Post-procedure bleeding occurs in up to 10% of patients
- Transabdominal CVS:
  - Done at 10 weeks gestation or later
  - The abdomen is cleansed with betadeine
  - A local anesthetic injection may be given
  - Using US to guide, a spinal needed is inserted through the abdomen into the uterine wall and into the placenta
  - The needle is moved back and forth several times through the placenta
  - Suction is used to remove the villi sample
  - This method is easiest when the placenta is anterior or away from the cervix
  - This method is better for women with a retroverted uterus
  - A smaller sample (pieces of villi) is taken as compared to transcervical CVS
  - The procedure is usually more uncomfortable than the transcervical method
  - Bleeding after the procedure is rare
- CVS takes approximately 5-7 minutes (not including prep time)
- The baby's heartbeat is monitored by US
- The collected sample is examined under the microscope to confirm that fetal tissue and not maternal tissue was collected
- If maternal cells were collected, the CVS will be repeated
- The sample is sent to the lab
- Results are available in approximately 10 days
What will it feel like?
- There may be some discomfort when the needle enters the skin and the uterus or when the catheter enters the cervix and placenta
- Some say that they feel pressure during the procedure
- You may experience a small amount of bleeding after CVS
What are the risks?
- The background rate of pregnancy loss at 10-12 weeks is 2-3%
- CVS increases the risk of miscarriage by 1/100 (1%) in women with a normal uterus
  - Reinforce that 99% of women will have a healthy baby
- CVS increases the risk of miscarriage by 5/100 (5%) in women with a retroverted uterus using transcervical CVS
- Some studies indicate an increased risk for limb defects when CVS is done before 10 weeks gestation
  - When performed at 10-12 weeks, most recent studies do not report an increased risk because limbs have already formed at this point
  - The risk is approximately 1/3000 (0.0003%)
- There are special considerations for mothers who are Rh negative. They need to take RhoGam after the CVS procedure
- There is a low risk of uterine infection
- Exercise or strenuous activity is to be avoided for 24 hours after the procedure
- Sexual intercourse, douching, tub baths, or tampon use are to be avoided for 72 hours after CVS procedure
- CVS is not recommended for women with the following:
  - Cervical polyps, overly curved sampling pathway, active genital herpes (for trans-cer)
  - Interceding bowel, placenta too far from abdomen surface (for trans-abd)
  - Active vaginal bleeding or bleeding disorder
- You should notify your doctor if any of the following occur:
  - Fever greater than 100.4 F
  - Heavy bleeding or cramping
  - Amniotic fluid leakage
Why should I choose CVS?
- CVS can be done earlier than amniocentesis (10-12 weeks versus 15-18 weeks)
- It may reduce a couples emotional stress if at risk for abnormality
- The procedure allows for termination at an earlier age
  - This is before the pregnancy is visible
  - Also before fetal movement is felt
- Allows for treatment of fetus affected with 21-hydroxylase deficiency
Why might I not want to choose CVS?
- There is a higher risk for pregnancy loss as compared to amniocentesis
  - 1% for CVS versus 0.5% for amnio
- CVS does not detect NTDs
- CVS is less commonly done as compared to amnio
- With CVS, there is a greater likelihood of needing further invasive testing due to:
  - Laboratory failure
  - Insufficient sample
  - Maternal cell contamination
    - Seen in approximately 1.9% of cases
  - Mosaic or ambiguous results
    - There are 2 or more cell types that are different genetically
    - Seen in 1-2% of CVS cases

Offer Resources

Literature, contact info, etc.
March of Dimes website

Elicit final questions and concerns

Reporting of the Results

If they are having the procedure, discuss how they would like to receive the results
- Appointment, phone call, etc.
- Who will contact them?
Discuss the options: elective abortion, adoption, etc.